Mirroring en SQL 2005

tengo los siguientes endpoints configurados en ambos extremos en 2 servers :

CREATE ENDPOINT [pruebaListener]
AUTHORIZATION [sa]
STATE=STARTED
AS TCP (LISTENER_PORT = 5023, LISTENER_IP = ALL)
FOR DATABASE_MIRRORING (ROLE = PARTNER, AUTHENTICATION = WINDOWS NEGOTIATE
, ENCRYPTION = DISABLED)


CREATE ENDPOINT [pruebaListener]
AUTHORIZATION [sa]
STATE=STARTED
AS TCP (LISTENER_PORT = 5023, LISTENER_IP = ALL)
FOR DATABASE_MIRRORING (ROLE = PARTNER, AUTHENTICATION = WINDOWS NEGOTIATE
, ENCRYPTION = DISABLED)

pero cuando presiono el boton start mirroring, me da el siguiente mensaje:

"Database mirroring transport is disabled in the endpoint configuration,
(microsot sql server.error 1486)"

alguna idea?